Alginate fibers have been known for use in surgical dressings for some time. UK 653,341 is an example of an early disclosure of the use of calcium alginate materials in surgical dressings. The earliest such materials were calcium alginate fibers, but they suffered from the disadvantage of being quite insoluble in water or wound exudate matter. Later a portion of the calcium ions in calcium alginate was substituted with other cations, whose alginate salts are soluble. UK 653,341 therefore proposed that some of the calcium ions be replaced with sodium ions, to form a mixed salt alginate.
Other uses for alginate fibers have been proposed which involve shaping the fibers as by weaving or knitting into sheets or pads. These materials are useful because they absorb water and swell but retain their shape and structural integrity.
Other polysaccharides have been proposed for fiber formation. For example, Burrow et al. (EP 232,121) have described cross-linked polysaccharides (starch, gellan, curdlan, pullulan, and glycogen) fibers. These cross-linked fibers are produced by extruding a dissolved carboxylate ester of the polysaccharide while simultaneously hydrolyzing the ester groups and cross-linking the resultant hydroxyl groups.
The extrusion of man-made fibers is known. Extrusion processes are known as melt, dry, and wet spinning. In melt spinning the molten polymer is extruded through a spinneret, which is a die perforated with tiny holes. The extruded material is cooled to form the fibers. Spinnerets of various hole sizes and cross-sections are used. Nylon, polyester, olefin and glass fibers are made by this method.
Dry spinning is used for acetate, triacetate, and acrylic fibers. In this process, the polymer is dissolved in an organic solvent and the extruded material is passed through a heated area to evaporate the solvent and form the fiber.
Wet spinning is used for rayon, spandex, and acrylics. In this process the dissolved polymer is extruded into a liquid bath where the fiber is coagulated or precipitated.
Maga et al., Intern'l J. of Food Sci. and Tech., 23, 49-56 (1988) have described the extrusion of various hydrocolloids at concentrations of up to 1% in combination with corn grits.